A pathological hallmark of Alzheimer disease and other tauopathies is the formation of neurofibrillary tangles mainly composed of bundles of fibrils formed by microtubule-associated protein Tau. Here we study the effects of Zn on abnormal aggregation and cytotoxicity of a pathological mutant ΔK280 of full-length human Tau. As revealed by Congo red binding assays, transmission electron microscopy, immunofluorescence, Western blot, and immunogold electron microscopy, pathological concentration of Zn dramatically accelerates the fibrillization of ΔK280 both in vitro and in SH-SY5Y neuroblastoma cells. As evidenced by annexin V-FITC apoptosis detection assay and MTT reduction assay, pathological concentration of Zn remarkably enhances ΔK280 fibrillization-induced apoptosis and toxicity in SH-SY5Y cells. Substitution of Cys-291 and Cys-322 with Ala, however, essentially eliminates such enhancing effects of Zn on the fibrillization and the consequent cytotoxicity of ΔK280. Furthermore, Zn is co-localized with and highly enriched in amyloid fibrils formed by ΔK280 in SH-SY5Y cells. The results from isothermal titration calorimetry show that Zn binds to full-length human Tau by interacting with Cys-291 and Cys-322, forming a 1:1 Zn-Tau complex. Our data demonstrate that zinc dramatically accelerates abnormal aggregation of human Tau and significantly increases Tau toxicity in neuronal cells mainly via bridging Cys-291 and Cys-322. Our findings could explain how pathological zinc regulates Tau aggregation and toxicity associated with Alzheimer disease.
It is desirable to experimentally demonstrate an extremely high resonant frequency, assisted by strain-spin coupling, in technologically important perpendicular magnetic materials for device applications. Here, we directly observe the coupling of magnons and phonons in both time and frequency domains upon femtosecond laser excitation. This strain-spin coupling leads to a magnetoacoustic resonance in perpendicular magnetic [Co/Pd]n multilayers, reaching frequencies in the extremely high frequency (EHF) band, e.g., 60 GHz. We propose a theoretical model to explain the physical mechanism underlying the strain-spin interaction. Our model explains the amplitude increase of the magnetoacoustic resonance state with time and quantitatively predicts the composition of the combined strain-spin state near the resonance. We also detail its precise dependence on the magnetostriction. The results of this work offer a potential pathway to manipulating both the magnitude and timing of EHF and strongly coupled magnon-phonon excitations.
We studied the tunnel magnetoresistance (TMR) of L1 0-FePd perpendicular magnetic tunnel junctions (p-MTJs) with an FePd free layer and an inserted diffusion barrier. The diffusion barriers studied here (Ta and W) were shown to enhance the TMR ratio of the p-MTJs formed using hightemperature annealing, which are necessary for the formation of high quality L1 0-FePd films and MgO barriers. The L1 0-FePd p-MTJ stack was developed with an FePd free layer with a stack of FePd/X/Co 20 Fe 60 B 20 , where X is the diffusion barrier, and patterned into micron-sized MTJ pillars. The addition of the diffusion barrier was found to greatly enhance the magneto-transport behavior of the L1 0-FePd p-MTJ pillars such that those without a diffusion barrier exhibited negligible TMR ratios (<1.0%), whereas those with a Ta (W) diffusion barrier exhibited TMR ratios of 8.0% (7.0%) at room temperature and 35.0% (46.0%) at 10 K after post-annealing at 350 C. These results indicate that diffusion barriers could play a crucial role in realizing high TMR ratios in bulk p-MTJs such as those based on FePd and Mn-based perpendicular magnetic anisotropy materials for spintronic applications.
Magnetic materials that possess large bulk perpendicular magnetic anisotropy (PMA) are essential for the development of magnetic tunnel junctions (MTJs) used in future spintronic memory and logic devices. The addition of an antiferromagnetic layer to these MTJs was recently predicted to facilitate ultrafast magnetization switching.Here, we report a demonstration of bulk perpendicular synthetic antiferromagnetic (p-SAF) structure comprised of an (001) textured FePd/Ru/FePd trilayer with a face-centered-cubic (fcc) phase Ruthenium spacer. The L1 0 -FePd p-SAF structure shows a large bulk PMA (K u~1 0.2 Merg/cm 3 ) and strong antiferromagnetic coupling (-J iec~2 .60 erg/cm 2 ). Full perpendicular magnetic tunnel junctions (p-MTJs) with L1 0 -FePd p-SAF layer were then fabricated. Tunneling magnetoresistance ratios of up to ~25% (~60%) are observed at room temperature (5 K) after post-annealing at 350 o C. Exhibiting high thermal stabilities and large K u , the bulk p-MTJs with a L1 0 -FePd p-SAF layer could pave a way for next-generation ultra-high-density and ultralow-energy spintronic applications.
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